This disclosure relates to the way in which container bodies (the so-called two-piece bodies) are manufactured in drawing and ironing operations. For 20 years beverage containers have been made in a drawing and ironing process in which the material is first cupped to establish the inside diameter and then pushed through a series of ironing rings which merely thin the side wall and do not appreciably affect the diameter. The process is done at high speed under a coolant/lubricant flood in order to accommodate the severity of the operation especially the heat. These containers have to be washed and in some cases chemically treated to remove residual lubricant and improve corrosion performance of organic coatings and decoration subsequently applied to the container.
For the last 25 years, work has progressed on manufacturing drawn cans for food products. These containers were made of materials such as aluminum and low temper steels in order to facilitate the drawing operation. In addition to this the containers usually had a height about equal to or less than the diameter of the container and the containers were fashioned in a single or at most two drawing operations.
The need for a drawn container is the elimination of the side seam and one double seamed bottom in a traditional 3-piece container. More specifically, to make a 3-piece can a flat blank of material is rolled into a cylinder and seamed along one side by welding, cementing or soldering. To this hollow cylindrical body is added a double seamed bottom closure. The cylindrical body may be precoated and the side seam area may be repaired by a stripe. The operations of side seaming and double seaming are such that the quality of the container is dependent upon those seams. Of course, the cylindrical body has to be flanged in order to accept the factory applied bottom and the packer applied top end closures. The flanging and seaming operations require some care and can cause problems especially in the area of the side seam.
Only recently has it been possible to make multiple drawn two piece food containers which were fashioned from organically precoated tin free steel such that postcoating or post treatment operations were not necessary. More particularly, a 24 oz. 404.times.307 tin free steel container was made in a two draw operation. (The can makers convention gives the diameter across the completed doubleseam in inches plus sixteenths of an inch then the height in inches plus sixteenths of an inch. Therefore, the foregoing container is 4 4/16" in diameter by 3 7/16" in height). It has long been desired to be able to make a container whose height is appreciably greater than the diameter, using precoated starting material in a multiple draw process. It is also desired to make such a container in the popular 16 oz. 303.times.406 size or the 15 oz. 300.times.407 size or the 11 oz. 211.times.400 size.
The Assignee of the present disclosure has recently manufactured and sold drawn containers in the 16 oz. size and the 15 oz. size and have experimentally produced the 10 oz. size using precoated stock. A triple draw operation was required to make the foregoing containers, and that process tends to thicken the area of the container side wall near the open end.
The amount of thickening increases from the bottom of the container to the top and all the way to the tip of the flange. This thickening is a consequence of the drawing of the material from a flat disc-shape and the variable circumferential compression of the material as a function of its distance from the bottom of the ultimately formed cup. The additional material thickness at the top of the container serves no useful purpose, and is a waste of material, increasing the weight and cost of the container.
Previous technology used in connection with drawing containers included a punch and die combination wherein there was sufficient annular clearance between the outer surface of the punch and the inner surface of the die so that metal was not squeezed or thinned during forming. These clearances were on the order of one and one-quarter to two times the thickness of the material being drawn (for the types of steel and aluminum used to make cans). Additionally, the draw die radius (or surface over which the metal was drawn) had a radius of curvature of less than 0.125" to facilitate the movement of metal through the die. The use of such tooling reformed the metal and allowed the thickening of the upper side wall of the ultimately formed hollow container as already discussed.
In contradistinction, the drawing and ironing (D&I) process used for making beverage containers would have less clearance than the original metal thickness between the ironing ring and the punch. More specifically, the difference between that clearance and the thickness of the metal represented the amount to which the side wall of the container was thinned. Usually, metal with no organic coating passes through three different ironing rings in a D&I operation during which the T-1 temper ETP electrolytic tinplate is reduced about 25% in the first pass, about 25% of its new thickness in the second pass, and about 40% of its new thickness in the last pass, while the metal and tooling are flooded with lubricant coolant. This operation increases the side wall length to several times that of the cup which was formed in an ordinary and separate one or two-draw operation. The cross-sectional configuration of the ironing ring includes a chamfer, a land and finally a relief angle. The ironing process begins on the chamfer and is completed by the land at this time no drawing takes place. The D&I process has heretofore been one in which drawing and ironing takes place in a coolant/lubricant flood. Coatings are normally applied after the shell has trimmed and washed free of lubricants. It was desired to concurrently draw and iron organically-precoated metal without having to remove the coolant/lubricant and to find a way for making a container with a uniform wall thickness.